Rotor and rotating electric machine

Abstract

A permanent magnet (23) of a rotor (20) has a folded-back shape that is convex inward in the radial direction. The permanent magnet is set such that a maximum stress load, which can cause cracking within the operating temperature range of the rotating electric machine, is applied at a return point (23b1) of a bent portion (23b). The permanent magnet includes a localized stress concentration region in the bent portion (23b).

Description

Rotor and Rotating Electric Machine Cross - reference to Related Applications 【0001】 This application is based on Japanese Application No. 2024 - 212133 filed on December 5, 2024, the contents of which are incorporated herein by reference. 【0002】 This disclosure relates to a rotor and a rotating electric machine. 【0003】 A rotating electric machine using an interior permanent magnet (IPM) type rotor is well - known. The interior permanent magnet type rotor has a configuration in which permanent magnets are embedded in an inner part rather than on the outer peripheral surface of the rotor core. The interior permanent magnet type rotor has a configuration in which, in addition to the magnet torque by the permanent magnets, a reluctance torque is obtained in an outer core part located outside the permanent magnets. 【0004】 As an example of a permanent magnet used for an interior permanent magnet type rotor, one having a folded shape that is convex toward the inner side in the radial direction is known. By making the shape of the permanent magnet fold at a deeper position toward the inner side in the radial direction, it is possible to enlarge the outer core part and also to obtain a configuration in which a larger reluctance torque can be obtained (see, for example, Patent Document 1). 【0005】 Japanese Patent Application Laid - Open No. 2021 - 197748 【0006】 The rotor core is generally configured, for example, as a laminated type of electromagnetic steel sheet, and the permanent magnet is generally configured, for example, as a resin - bonded type bonded magnet. Therefore, they are generally made of materials having significantly different thermal expansion coefficients from each other. Therefore, due to changes in heat acting on the rotor, cracks may occur in the permanent magnet. In this case, if a crack occurs in a location where a large amount of effective magnetic flux of the permanent magnet is generated, there is a concern that it may affect the output of the rotating electric machine. Therefore, it is desirable to avoid cracks in locations where the permanent magnet cannot be overlooked as much as possible. 【0007】The object of this disclosure is to provide a rotor and a rotating electric machine that can minimize the impact on the output of the rotating electric machine even if a crack occurs or is likely to occur in the permanent magnet. The rotor according to a first aspect of this disclosure is an embedded magnet type rotor provided in a rotating electric machine, comprising a rotor core having magnet housing holes, and permanent magnets provided in the magnet housing holes by filling with magnetic material, wherein the permanent magnets have a radially inward convex folded shape with a bent portion on the radially inward side of the rotor, the permanent magnets are set so that the maximum stress load at which a crack can occur within the operating temperature range of the rotating electric machine is applied at the folding point of the bent portion, and the permanent magnets include a localized stress concentration point in the bent portion. 【0008】 A second aspect of the present disclosure is a rotating electric machine comprising an embedded magnet type rotor having permanent magnets provided by filling magnet housing holes of a rotor core with magnetic material, and a stator that applies a rotating magnetic field to the rotor, wherein the permanent magnets of the rotor have a radially inwardly convex folded shape with a bent portion on the radially inward side of the rotor, the permanent magnets are set so that the maximum stress load at which cracks can occur within the operating temperature range of the rotating electric machine is applied at the folding point of the bent portion, and the permanent magnets include a localized stress concentration point in the bent portion. 【0009】 According to the rotor and rotating electric machine configuration described above, in the embedded magnet type rotor, the permanent magnets have a convex folded shape radially inward, and the maximum stress load at which cracks can occur within the operating temperature range of the rotating electric machine is applied to the folding point of the bend. In other words, because the permanent magnets are configured to include localized stress concentration points in the bend, cracks can actively occur in areas where effective magnetic flux is low. This makes it possible to minimize the impact on the output of the rotating electric machine. 【0010】The above-mentioned and other purposes, features and advantages of this disclosure will be further clarified by the following detailed description with reference to the attached drawings. The drawings are as follows: Figure 1 is a configuration diagram showing a rotating electric machine including a rotor in one embodiment; Figure 2 is a configuration diagram showing a rotor in the same embodiment; Figure 3 is a configuration diagram showing a rotor in the same embodiment; Figure 4 is a perspective view showing a rotor in the same embodiment; Figure 5 is an explanatory diagram of the configuration of a permanent magnet in the same embodiment; Figure 6 is an explanatory diagram of the configuration of a permanent magnet in the same embodiment; Figure 7 is an explanatory diagram of the configuration of a permanent magnet in the same embodiment; Figure 8 is a configuration diagram showing a rotor in a modified example; Figure 9 is a configuration diagram showing a rotor in a modified example; Figure 10 is a configuration diagram showing a rotor in a modified example; and Figure 11 is a configuration diagram showing a rotor in a modified example. 【0011】 The following describes one embodiment of the rotor and the rotating electric machine. (Rotating electric machine M, stator 10) The rotating electric machine M of this embodiment shown in Figure 1 is composed of an embedded magnet type brushless motor. The rotating electric machine M comprises a substantially annular stator 10 and a substantially cylindrical rotor 20 that is rotatably arranged in the radially inner space of the stator 10. 【0012】 The stator 10 is equipped with a substantially annular stator core 11. The stator core 11 is made of a magnetic metal material, for example, by stacking multiple sheets of cold-rolled steel (SPCC) electromagnetic steel sheets in the axial direction. In this embodiment, the stator core 11 has 12 teeth 12 that extend radially inward and are arranged at equal intervals in the circumferential direction. Windings 13 are wound around each tooth 12 in a concentrated winding manner, and are connected in three phases so that they function as U-phase, V-phase, and W-phase magnetic poles, respectively. The stator 10 applies a rotating magnetic field to the rotor 20 based on the power supply to the windings 13 of each phase, thereby driving the rotor 20 to rotate. In this stator 10, the outer circumferential surface of the stator core 11 abuts against the inner circumferential surface of the housing 14 and is fixed in place. 【0013】(Rotor 20, Rotor Core 22) As shown in Figures 1 and 2, the rotor 20 comprises a rotating shaft 21, a substantially cylindrical rotor core 22 into which the rotating shaft 21 is fitted in the center, and eight permanent magnets 23 embedded inside the rotor core 22 in this embodiment. The rotor core 22 is made of a magnetic metal material, for example, it is made by stacking multiple electromagnetic steel sheets in the axial direction, similar to the stator core 11. The rotor 20 is rotatably positioned relative to the stator 10 by the rotating shaft 21 being supported by a bearing (not shown) provided in the housing 14. 【0014】 The rotor core 22 has magnet housing holes 24 for housing permanent magnets 23. In this embodiment, eight magnet housing holes 24 are provided at equal intervals in the circumferential direction of the rotor core 22. Each magnet housing hole 24 has a roughly V-shaped folded back form that is convex radially inward, and all of them have the same shape. Furthermore, the magnet housing holes 24 are provided along the entire axial direction of the rotor core 22. 【0015】 (Permanent Magnet 23) The permanent magnet 23 of this embodiment is a resin-bonded type bonded magnet made by mixing and bonding magnetic powder with resin. The permanent magnet 23 is constructed by using the magnet housing hole 24 of the rotor core 22 as a mold, filling the magnet housing hole 24 without gaps by injection molding before solidification, and then solidifying it inside the magnet housing hole 24 after filling. Therefore, the shape of the hole in the magnet housing hole 24 becomes the outer shape of the permanent magnet 23. As the magnetic powder used in the permanent magnet 23 of this embodiment, for example, samarium iron nitrogen (SmFeN) type magnet is used, but other rare earth magnets may also be used. 【0016】As shown in Figure 2, the permanent magnet 23 has a shape in which the radially inner ends of a pair of straight sections 23a are connected by a bent section 23b, forming a roughly V-shaped folded back shape that is convex radially inward. In this embodiment, the radially outer end 23c of the straight section 23a of the permanent magnet 23 is located near the outer circumferential surface 22a of the rotor core 22, and the bent section 23b is located radially inward, close to the shaft insertion hole 22b in the center of the rotor core 22 into which the rotating shaft 21 is inserted. The permanent magnet 23 has a shape that is symmetrical with respect to its own circumferential center line Ls passing through the axis center O1 of the rotor 20, and is close to the magnetic pole boundary line Ld passing through the axis center O1 of the rotor 20 between adjacent permanent magnets 23. The angle between adjacent magnetic pole boundary lines Ld, that is, the magnetic pole opening angle θm of the rotor magnetic pole section 26 including this permanent magnet 23, is 180° in electrical angle. 【0017】 Here, the distance between the extension lines of the inner surfaces of each straight section 23a of the V-shaped permanent magnet 23 and the outer surface 22a of the rotor core 22 is defined as the magnetic pole pitch Lp, and the distance from the outer surface 22a of the rotor core 22 to the inner surface of the bent section 23b on the circumferential center line Ls of the permanent magnet 23 is defined as the embedding depth Lm. The permanent magnet 23 in this embodiment is set to have a deep folded shape such that the embedding depth Lm is greater than the magnetic pole pitch Lp. In other words, the magnet surface 23x of the permanent magnet 23 in this embodiment, formed by the inner surfaces of each straight section 23a and bent section 23b, is set to be larger than the magnet surface of a well-known surface magnet type (not shown). Note that this folded shape of the permanent magnet 23 is just one example, and can be changed as appropriate, such as having a shallower embedding depth Lm or a roughly U-shaped folded shape with a large bent section 23b. 【0018】Furthermore, with respect to the permanent magnet 23, the pair of straight sections 23a in the V-shaped path are set to a constant thickness Wm. The bent section 23b is set to the smallest thickness Wm1 at the turning point 23b1. The thickness Wm1 of the bent section 23b1 at the turning point 23b1 is smaller than the thickness Wm of the straight section 23a. The bent section 23b has a gradually changing shape, with its thickness decreasing from the part connecting to the straight section 23a towards the turning point 23b1. The gradually changing shape of the bent section 23b is achieved by making the curvature of the outer surface greater than the curvature of the inner surface of the bent section 23b. Permanent magnets 23 having such an axial shape are provided in the magnet housing hole 24 of the rotor core 22, extending along the entire axial direction. 【0019】 The magnetic material of the permanent magnets 23, which are filled into the magnet housing holes 24 of the rotor core 22, is unmagnetized at the time of filling. After the magnetic material is filled into the magnet housing holes 24 and solidified, magnetization is performed from outside the rotor core 22 using a magnetization device (not shown), and after magnetization, it functions as a permanent magnet 23. In this embodiment, eight permanent magnets 23 are provided in the circumferential direction of the rotor core 22, and they are magnetized so that they alternately have opposite poles in the circumferential direction. In addition, each individual permanent magnet 23 is magnetized in its own thickness direction. 【0020】 The portion of the rotor core 22 located inside the V-shaped folded form of the permanent magnet 23 and radially outward from the permanent magnet 23 functions as an outer core portion 25 for obtaining reluctance torque in opposition to the stator 10. The outer core portion 25 has a substantially triangular shape with one vertex pointing towards the center of the rotor 20 in an axial view. In this embodiment, the rotor 20 is configured as an 8-pole rotor magnetic pole portion 26, including the permanent magnet 23 and the outer core portion 25 surrounded by the inside of the V-shape of the permanent magnet 23. Each rotor magnetic pole portion 26 functions alternately as a north pole and a south pole in the circumferential direction, as shown in Figure 1. In a rotor 20 having such a rotor magnetic pole portion 26, magnet torque and reluctance torque can be suitably obtained. 【0021】(End Plates 27) As shown in Figure 4, the rotor 20 is further provided with a pair of end plates 27. The end plates 27 are made of, for example, a non-magnetic metal material and are disc-shaped with the same diameter as the rotor core 22. The end plates 27 are mounted so as to be able to rotate integrally with the rotor core 22 or the rotating shaft 21, so as to abut against both axial ends of the rotor core 22. The end plates 27 close the openings on both axial sides of the magnet housing holes 24 of the rotor core 22. Each end plate 27 closes the openings of multiple magnet housing holes 24 collectively. The end plates 27 have the function of preventing the scattering of fragments of the permanent magnet 23 and the detachment of the permanent magnet 23 in the event that a permanent magnet 23 in the magnet housing hole 24 is chipped and fragments are generated, or that a permanent magnet 23 is broken and comes out in the axial direction. 【0022】 (Operation of this embodiment) The operation of this embodiment will now be described. In the rotor 20, the rotor core 22 made of electromagnetic steel sheet and the permanent magnet 23 made of bonded magnet are made of commonly used materials, but they are materials with significantly different coefficients of thermal expansion. Therefore, cracks may occur in the permanent magnet 23 due to sudden changes in the heat acting on the rotor 20 or repeated thermal changes. If cracks occur in the area of ​​the permanent magnet 23 that generates a large amount of effective magnetic flux, it may affect the output of the rotating electric machine M. In this embodiment, the configuration of the permanent magnet 23 has been devised to avoid this as much as possible. 【0023】As shown in Figures 2 and 3, the permanent magnet 23 of this embodiment is configured such that the thickness of the bent portion 23b is smaller than the thickness Wm of the straight portion 23a. The bent portion 23b also has a gradually decreasing thickness towards the turning point 23b1, with the smallest thickness Wm1 at the turning point 23b1. In other words, the shape is designed so that the stress concentration points of the permanent magnet 23 are in the bent portion 23b rather than the straight portion 23a, and especially in the vicinity of the turning point 23b1. The straight portion 23a of the permanent magnet 23 is a part where a lot of effective magnetic flux is generated, while the bent portion 23b is a part where a lot of effective magnetic flux is generated. Furthermore, the turning point 23b1 is the part of the bent portion 23b where the least effective magnetic flux is generated. Stress concentration points are set in areas where the amount of effective magnetic flux is low. Stress concentration points are also areas where cracks CR are likely to occur (see Figure 3). Cracks CR occur along the thickness direction of the permanent magnet 23. 【0024】 Figure 5 shows the relationship between the thickness of the permanent magnet 23 and the maximum stress load. In this embodiment, the permanent magnet 23 has a thickness set such that the area including the fold point 23b1 of the bent portion 23b is a stress concentration point, and the maximum stress load that is applied is used as a guideline (indicated as the crack guideline in the figure) for when a crack CR may occur within the operating temperature range of the rotating electric machine M. In other words, a large stress load is intentionally applied to the fold point 23b1 of the bent portion 23b of the permanent magnet 23 or its vicinity, so that a crack CR may occur in the bent portion 23b early after the permanent magnet 23 is manufactured, for example, before the rotating electric machine M is put into use. The operating temperature range is, for example, -40°C to 120°C. 【0025】 Figure 6 shows the relationship between crack width and change in effective magnetic flux. The width of the crack CR is approximately 10 [μm]. Due to the structure of the permanent magnet 23 of this embodiment, which is installed in the closed space within the magnet housing hole 24, the crack width is at most approximately 50 [μm]. The change in effective magnetic flux (or induced voltage ratio) remains almost constant up to a crack width of approximately 200 [μm], and when it exceeds 200 [μm], the decrease tends to increase as well. From this, it can be seen that even if a crack CR occurs in the assumed location of the bent portion 23b of the permanent magnet 23, the effect on the output of the rotating electric machine M is extremely small. 【0026】 Figure 7 shows the effective magnetic flux quantities of this embodiment (referred to as the present invention in the figure) and the first and second comparative examples. The first comparative example has a 0.4 mm (400 μm) non-magnetic spacer interposed at the folding point 23b1. The second comparative example has a 0.4 mm (400 μm) magnetic bridge at the folding point 23b1. As already mentioned in relation to the size of the crack width in Figure 6, the crack CR that may occur in the permanent magnet 23 of this embodiment has a sufficiently small effect on the effective magnetic flux quantity, that is, on the output of the rotating electric machine M, compared to the other comparative examples. 【0027】 In this embodiment, the crack CR is designed to actively form at the assumed location of the bent portion 23b of the permanent magnet 23, thereby sufficiently mitigating stress concentration that could lead to cracking in the straight portion 23a, which has a significant impact on the output of the rotating electric machine M. 【0028】 (Effects of this embodiment) The effects of this embodiment will now be described. (1) In the rotor 20 of this embodiment, the permanent magnet 23 has a radially inward convex folded shape, and the maximum stress load at which a crack CR can occur within the operating temperature range of the rotating electric machine M is applied to the folding point 23b1 of the bent portion 23b. In other words, since the bent portion 23b of the permanent magnet 23 is configured to include a localized stress concentration point, a crack CR can be actively generated in a part where the effective magnetic flux generation is low. As a result, even if a crack CR occurs in the permanent magnet 23 or is likely to occur, the impact on the output of the rotating electric machine M can be kept to a minimum. Incidentally, when a crack CR does not occur in the permanent magnet 23, a stress load is applied to the permanent magnet 23. When a crack CR occurs in the permanent magnet 23, the stress load applied to the permanent magnet 23 becomes sufficiently small. 【0029】 Furthermore, in this embodiment, it is considered acceptable for a crack CR to have already formed in the bent portion 23b of the permanent magnet 23 before the rotating electric machine M is put into use. This is because the formation of a crack CR in the bent portion 23b sufficiently alleviates the stress concentration that would lead to cracking in the straight portion 23a, which has a large impact on the output of the rotating electric machine M. 【0030】(2) The permanent magnet 23 has a gradually changing shape in which its thickness gradually decreases toward the folding point 23b1 of the bent portion 23b, making it easy to create stress concentration points. (3) Since end plates 27 that close the axial openings of the magnet housing holes 24 are arranged at the axial ends of the rotor core 22, even if a crack CR occurs in the permanent magnet 23, it is possible to prevent the scattering of fragments of the permanent magnet 23 and the permanent magnet 23 from coming out. In addition, since the end plates 27 close the openings of multiple magnet housing holes 24 at each axial end of the rotor core 22 all at once, the openings can be easily closed. 【0031】 (Example of modification) This embodiment can be implemented with the following modifications. This embodiment and the following examples of modifications can be combined with each other to the extent that they do not contradict each other technically. 【0032】 - In the above embodiment, the permanent magnet 23 uses a gradually changing shape in which the thickness gradually decreases toward the folding point 23b1 as an example of a configuration that concentrates stress in a local region including the folding point 23b1 of the bent portion 23b, but this may be changed as appropriate. For example, it may be as shown in the first to fourth modified examples below. 【0033】 In the first modification example shown in Figure 8, a recess 23b2 is provided that is recessed in the thickness direction from the inner surface of the bent portion 23b. In the second modification example shown in Figure 9, a recess 23b3 is provided that is recessed in the thickness direction from the outer surface of the bent portion 23b. In the third modification example shown in Figure 10, recesses 23b2 and 23b3 are provided on the inner surface and outer surface of the bent portion 23b, respectively. In each modification example shown in Figures 8 to 10, the thickness of the folding point 23b1 of the bent portion 23b is locally reduced, so that stress concentration occurs at or near the folding point 23b1. In each modification example, a stress concentration point can be easily created, and even if a crack CR occurs or is likely to occur in the permanent magnet 23, it is expected that the impact on the output of the rotating electric machine M will be kept to a minimum. 【0034】In the fourth modification example shown in Figure 11, not only is the shape of the permanent magnet 23 improved as described above, but the way the magnetic material is filled into the permanent magnet 23 is also improved. A pair of filling holes 28 are set at positions equidistant from the turning point 23b1, and the weld line WL is set to be the turning point 23b1. The weld line WL is a place where stress concentration can occur and may later propagate into a crack CR. In this modification example as well, even if a crack CR occurs or will occur in the permanent magnet 23, it is expected that the impact on the output of the rotating electric machine M will be kept to a minimum. Furthermore, this can be easily addressed simply by improving the way the magnetic material is filled into the permanent magnet 23. In this modification example, it is applied to a gradually deforming shape in which the thickness of the bent portion 23b is gradually reduced toward the turning point 23b1, but it can also be applied to a shape in which the bent portion 23b has the same constant thickness Wm, similar to the straight portion 23a. 【0035】 The V-shaped folded form of the permanent magnet 23 in the above embodiment is just one example, and may be modified as appropriate, such as having a shallower V-shaped embedding depth Lm of the permanent magnet 23 or a roughly U-shaped folded form with a larger bend 23b. 【0036】 - In the above embodiment, the permanent magnet 23 was a bonded magnet using samarium iron nitrogen-based magnet powder, but other rare earth magnet powders or magnet powders other than rare earth may be used. - In addition to the above, the configuration of the rotor 20, the stator 10, and the rotating electric machine M may be changed as appropriate. 【0037】 This disclosure is described in accordance with the embodiments, but it is understood that this disclosure is not limited to such embodiments or structures. This disclosure also includes various modifications and variations within the equivalence. In addition, various combinations and forms, as well as other combinations and forms that include only one, more, or fewer of those elements, fall within the scope and concept of this disclosure. 【0038】(Note) The technical concepts that can be understood from the above embodiments and modified examples are described below. [1] A rotor (20) of the embedded magnet type to be provided in a rotating electric machine (M), comprising: a rotor core (22) having magnet housing holes (24); and a permanent magnet (23) provided in the magnet housing holes by filling with magnetic material, wherein the permanent magnet has a radially inwardly convex folded shape with a bent portion (23b) on the radially inward side of the rotor, the permanent magnet is set so that the maximum stress load that can cause a crack (CR) to occur at the folding point (23b1) of the bent portion within the operating temperature range of the rotating electric machine is applied, and the permanent magnet includes a localized stress concentration point in the bent portion. 【0039】 [2] The rotor according to [1] above, wherein the permanent magnet has a gradually changing shape in which the thickness gradually decreases toward the turning point of the bent portion, or the stress concentration point is formed by providing recesses (23b2, 23b3) that are recessed in the thickness direction. 【0040】 [3] The rotor according to [1] or [2] above, wherein the stress concentration point is formed in the permanent magnet by positioning a weld line (WL) formed by filling the magnetic material at the folding point of the bent portion. 【0041】 [4] The rotor according to any one of [1] to [3] above, wherein the magnet housing hole of the rotor core is closed by an end plate (27) whose axial opening is located at the axial end of the rotor core. 【0042】 [5] The rotor according to any one of the above items [1] to [4], wherein the permanent magnet has already developed the crack before the rotating electric machine (M) is put into use. 【0043】 [6] The rotor according to [5], wherein the crack occurring in the permanent magnet has a width less than 200 [μm]. 【0044】[7] A rotating electric machine (M) comprising: an embedded magnet type rotor (20) having permanent magnets (23) provided by filling magnet housing holes (24) of a rotor core (22) with magnetic material; and a stator (10) that applies a rotating magnetic field to the rotor, wherein the permanent magnets of the rotor have a radially inwardly convex folded shape with a bent portion (23b) on the radially inward side of the rotor; the permanent magnets are set such that the maximum stress load at which a crack (CR) can occur within the operating temperature range of the rotating electric machine can occur at the folding point (23b1) of the bent portion; and the permanent magnets include a localized stress concentration point in the bent portion.

Claims

1. A rotor (20) of the embedded magnet type to be installed in a rotating electric machine (M), comprising: a rotor core (22) having magnet housing holes (24); and permanent magnets (23) provided in the magnet housing holes by filling with magnetic material, wherein the permanent magnets have a radially inwardly convex folded shape with a bent portion (23b) on the radially inward side of the rotor, the permanent magnets are set such that the maximum stress load at which a crack (CR) can occur within the operating temperature range of the rotating electric machine is applied to the folding point (23b1) of the bent portion, and the permanent magnets include a localized stress concentration point in the bent portion.

2. The rotor according to claim 1, wherein the permanent magnet has a gradually changing shape in which its thickness gradually decreases toward the turning point of the bent portion, or the stress concentration point is formed by providing recesses (23b2, 23b3) that are recessed in the thickness direction.

3. The rotor according to claim 1, wherein the stress concentration point is formed in the permanent magnet by positioning a weld line (WL) formed by filling the magnetic material at the folding point of the bent portion.

4. The rotor according to claim 1, wherein the magnet housing hole of the rotor core is closed by an end plate (27) whose axial opening is located at the axial end of the rotor core.

5. The rotor according to claim 1, wherein the permanent magnet already has the crack present before use by the rotating electric machine (M).

6. The rotor according to claim 5, wherein the crack occurring in the permanent magnet has a width less than 200 [μm].

7. A rotating electric machine (M) comprising: an embedded magnet type rotor (20) having permanent magnets (23) provided by filling magnet housing holes (24) of a rotor core (22) with magnetic material; and a stator (10) that applies a rotating magnetic field to the rotor, wherein the permanent magnets of the rotor have a radially inwardly convex folded shape with a bent portion (23b) on the radially inward side of the rotor; the permanent magnets are set such that the maximum stress load at which a crack (CR) can occur within the operating temperature range of the rotating electric machine can occur at the folding point (23b1) of the bent portion; and the permanent magnets include a localized stress concentration point in the bent portion.

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